WHICH  HAVE  CONSOLIDATED  ON  STEEP  SLOPES. 
779 
fine  specimens  in  a fresh  state  not  differing  in  the  slightest  particular  from  the  Nizzeti 
fossil 
Omitting  this  shell,  we  have  eleven  species  out  of  142  which  are  extinct ; but  when 
we  endeavour  to  estimate  the  relative  age  of  this  formation,  we  must  take  into  account 
not  only  the  comparative  number  of  hving  and  extinct  species,  but  also  the  relative 
number  of  individuals  by  which  each  species  is  represented.  We  then  find  that  although 
the  ground  in  most  of  the  localities  above  enumerated  is  plentifully  strewed  over,  espe- 
cially after  it  has  been  washed  by  heavy  rains,  with  fossil  shells,  not  one  of  the  extinct 
species,  except  Buccinum  semistriatum,  is  met  with  in  abundance.  Buccinum  musimm 
is  rare ; and  as  for  the  other  nine,  they  are  so  excessively  scarce,  that  most  of  them,  if 
not  all,  are  only  known  as  yet  by  single  individuals.  It  is  true  that  the  same  may  be 
said  of  some  few  even  of  the  recent  species,  but  the  larger  proportion  of  that  class  are 
very  common.  I never  succeeded,  when  collecting  myself  at  Cefali,  Aci  Gastello,  Trezza, 
and  Nizzeti,  during  my  three  visits  to  Etna  in  1828, 1857,  and  1858,  in  picking  up  with 
my  own  hands  any  of  the  extinct  species,  except  Buccinum  semistriatum  and  B.  musimim. 
In  regard  to  two  others  of  the  eleven  shells  enumerated  by  Dr.  Aeadas  as  extinct, 
namely,  Pyrula  rusticola  and  Monodonta  elegans,  Fauj.,  of  each  of  which  single  indivi- 
duals only,  and  those  not  in  a perfect  state,  have  been  found,  M.  Deshayes  observed  to 
me  that  they  agree  perfectly  in  form  and  appearance  with  well-known  Miocene  fossils 
which  he  has  received  from  Bordeaux ; he  therefore  asked  whether  some  mistake  may 
not  have  been  made,  or  if  not,  whether  they  might  not  have  been  washed  out  of  an  older 
tertiary  formation  in  the  neighbourhood  and  imbedded  in  the  Nizzeti  clays.  In  answer 
to  this  latter  suggestion,  it  would,  1 think,  be  difficult  so  to  explain  away  their  presence  ; 
for  the  only  other  strata  which  I saw  containing  tertiary  shells  near  the  base  of  Etna 
occurred  at  the  distance  of  about  fifteen  miles  from  Nizzeti,  nearly  due  north,  on  the 
banks  of  the  river  Menessah,  about  three  miles  W.S.W.  of  Piedemonte.  Here  I obtained 
a sufficient  number  of  species  to  satisfy  me  that  the  strata  were  older  than  those  of 
Nizzeti  and  Cefali,  although  by  no  means  referable  to  the  Miocene  era,  but  belonging 
rather  to  some  Newer  Pliocene  beds,  more  ancient  than  the  clays  of  Nizzeti. 
In  the  Appendix  C.  (page  786)  will  be  found  a second  list  of  62  species  of  Mollusca 
and  3 Echinoderms  from  Catira,  above  mentioned,  p.  777,  given  me  by  Signor  Gaetano 
G.  Gemmellako,  by  whom  they  were  collected  and  named.  Excluding  five  of  the  species 
of  mollusca,  which  Signor  Gemmellako  could  not  determine  specifically,  there  would 
* Murex  vaginatus  is  one  of  the  few  species  on  which  some  Italian  geologists  have  relied  for  proving  the 
antiquity  of  the  marls  of  the  volcanic  island  of  Ischia,  near  Naples,  to  be  much  greater  than  that  which  I 
assigned  to  them  after  my  visit  to  Naples  in  1828.  (See  Bulletin  de  la  Soc.  Geol.  de  France,  tom.  xi.  2nd 
ser.  p.  72,  and  tom.  xiii.  p.  285,  and  xxv.  p.  362.)  In  the  first  edition  of  my  ‘ Principles  of  Geology,’  I 
classed  these  marls  as  Newer  Pliocene  (see  Table,  vol.  iii.  p.  61  and  p.  126),  and  having  re-examined  Ischia 
in  1857,  I maintain  the  correctness  of  my  published  opinion,  namely,  that  these  greenish  and  bluish  marls, 
about  1700  feet  above  the  sea,  belong,  like  the  sub-Etnean  marine  clays  above  described,  to  the  new'est  part 
of  the  Newer  Pliocene  period.  To  class  them  therefore  as  suh-Apennine  or  Older  Pliocene,  would  be  a 
serious  retrograde  movement,  and  one  against  which  I am  glad  to  see  that  M.  Puggaaed  has  protested. 
Bulletin,  2™®  ser.  tom.  xiv.  p.  336. 
